Inhibitor of the inflammatory response induced by the TNFA and IL-1

ABSTRACT

The present invention provides the molecular basis for cytokine induction of NF-κB-dependent immune and inflammatory responses, emphasizing a role for both NIK-NIK and NIK-IKK protein-protein interactions. A relatively small region of NIK selectively impairs the NIK-IKK interaction. The present invention provides a highly specific method for modulating NF-κB-dependent immune, inflammatory, and anti-apoptotic responses, based on interruption of the critical protein-protein interaction of NIK and IKK. The present invention provides methods for inhibiting NF-κB-dependent gene expression, using mutant NIK proteins. One embodiment of the present invention provides kinase-deficient NIK mutant proteins that inhibit activation of IKK. Another embodiment of the invention provides N-terminus NIK mutant proteins that bind IKK, thus inhibiting NIK/IKK interaction.

This application claims priority of U.S. Ser. No. 60/076,299, filed Feb. 27, 1998.

Throughout this application various publications are referenced. The disclosures of these publications in their entireties are hereby incorporated by reference into this application in order to more fully describe the state of the art to which this invention pertains.

FIELD OF INVENTION

The present invention relates generally to the field of NF-κB-dependent activation to regulate immune, inflammatory, and anti-apoptotic responses. In particular, the present invention describes an inhibitor of serine/threonine kinase signaling that regulates NF-κB-dependent activation, thereby regulating immune, inflammatory, and anti-apoptotic responses. The present invention describes several mutant proteins of the NF-κB-inducing kinase (NIK) that prevent activation of a downstream kinase, IκB-specific kinase (IKK). One embodiment of the present invention describes kinase-deficient mutant NIK proteins that inhibits phosphorylation and activation of IKK. Another embodiment of the present invention describes an C-terminal NIK peptide protein that effectively interacts with IKK, and blocks IKK activation by inhibiting NIK/IKK association. Yet another embodiment of the present invention describes a method for inhibiting NF-κB-dependent immune and inflammatory responses using the NIK mutant proteins.

BACKGROUND OF THE INVENTION

TNFα (tumor necrosis factor alpha) binding at the plasma membrane induces intracellular signaling events that translate into the induction of NF-κB in the nucleus. The eukaryotic NF-κB/Rel (nuclear factor-κB/Rel) family of transcription factors plays an essential role in the regulation of inflammatory, immune, and apoptotic responses (Bacuerle and Baltimore 1996; Baldwin 1996; Verma et al 1995). One of the distinguishing characteristics of the NF-κB/Rel transcription factor is its post-translational regulation through interactions with cytoplasmic inhibitory proteins termed IκB (inhibitor-κB). NF-κB corresponds to an inducible eukaryotic transcription factor complex that is negatively regulated in resting cells, by its physical assembly with a family of cytoplasmic ankyrin-rich IκB inhibitors (Bacuerle and Baltimore 1996; Baldwin 1996; Verma et al 1995). Stimulation of cells with various pro-inflammatory cytokines, including TNFα, induces nuclear NF-κB expression. The TNFα-signaling pathway is complex and involves recruitment of at least three adapter proteins, TRADD (TNF-R1 associated death domain protein) and TRAF-2 (TNF-receptor-associated factor)-2, and the serine/threonine kinase RIP (receptor interacting protein) to the cytoplasmic tail of the type 1 TNF receptor (Hsu et al Immunity 1996; Hsu et al Cell 1996) (FIG. 1). In turn, the recruitment of these factors promotes activation of the downstream NIK (Malinin et al 1997) and IKKα and IKKβ (IκB-specific kinases) (DiDonato et al 1997; Mercurio et al 1997; Regnier et al 1997; Woronicz et al 1997; Zandi et al 1997). The activated IKKα and IKKβ directly phosphorylates the two N-terminal regulatory serines within IκBα, triggering ubiquitination and rapid degradation of this inhibitor in the 26S proteasome (Bacuerle and Baltimore 1996; Baldwin 1996; Verma et al 1995). Degradation of IκBα unmasks the nuclear localization signal on NF-κB, allowing the NF-κB to translocate to the nucleus where it engages cognate κB enhancer elements and activates the transcription of various κB-dependent genes involved in inflammatory, immune, and anti-apoptotic responses.

IL-1, a second proinflammatory cytokine, acts in a manner similar to TNFα. IL-1 binding to its receptor recruits the MyD88 and TRAF-6 adapter proteins and (IRAK), a serine-threonine kinase (Cao et al 1996; Muzio et al 1997). Like TRAF-2, TRAF-6 interacts with NIK. Thus, the TNFα and IL-1 signaling pathways converge at the level of NIK. The present invention provides new insights into the molecular basis for NIK regulation of NF-κB-dependent gene expression, and provides novel methods for modulating NF-κB-dependent immune, inflammatory, and anti-apoptotic responses.

SUMMARY OF THE INVENTION

The present invention provides a molecular mechanism to interfere with cytokine induction of NF-κB-dependent immune, inflammatory, and anti apoptotic responses, through interference with the assembly of NIK and the IKK proteins. A relatively small region of NIK selectively impairs the NIK-IKK interaction. The present invention provides a novel and highly specific method for modulating NF-κB-dependent immune and inflammatory responses, based on interruption of the critical protein-protein interaction of NIK and IKK. The present invention provides methods for inhibiting NF-κB-dependent gene expression, using mutant NIK proteins. One embodiment of the present invention provides kinase-deficient NIK mutant proteins that inhibit activation of IKK. Another embodiment of the invention provides N-terminus NIK mutant proteins that bind IKK, thus inhibiting NIK/IKK interaction.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1: Schematic summary of the overlapping and unique intracellular signaling pathways including adapter molecules and specific kinases activated by the proinflammatory cytokines TNFα and IL-1.

FIG. 2: A) Alignment of the amino acid sequences of the activation loop between subdomains VII (DFG) and VIII (M(A/S)PE) of NIK and other MAP kinases. Asterisks denote residues shown to be phosphorylated and/or implicated in the activation of these kinases. B) Biological function of wild-type NIK and kinase domain mutant forms of NIK. C) In vivo phosphorylation of wild-type NIK and the mutant forms of NIK.

FIG. 3: A) The NIK-T559A mutant protein fails to activate IKKα- and kinase activity. B) The NIK-T559A mutant protein fails to induce κB-luciferase activity. C) The expression of NIK-T559A mutant protein dominantly interferes with TNFα-induced NF-κB activation in a dose-related manner.

FIG. 4: A) The NIK-T559A mutant protein assembles with IKKα but fails to phosphorylate coimmunoprecipitated IKKα. B) the NIK-T559A mutant protein fails to undergo auto phosphorylation.

FIG. 5: A) Biologically active NIK spontaneously forms homotypic oligomers in vivo. B) Myc-NIK and NIK-T7 proteins are expressed at comparable levels in transfected cultures.

FIG. 6: A) Schematic overview of the structural organization of NIK protein. B) Myc-NIK is stably expressed in transfected 293 cells. C) Multiple domains of NIK participate in homotypic oligomerization.

FIG. 7: A) Analysis of the functional effects of various deletion mutant forms of NIK in the presence and absence of TNFα. B) Analysis of the functional effects of various deletion mutant forms of NIK in the presence and absence of wild-type NIK protein. C) Analysis of the inhibitory effect of the C-terminus of NIK (amino acid residues 735 to 947) and shorter fragments (735-813, 814-947, 847-947) on TNFα (left graph) and NIK (right graph) induction of κB-luciferase activity.

FIG. 8: A) All the deletion forms of Myc-NIK are comparably expressed when cotransfected with T7-IKKα. B) The C-terminus of NIK mediates heterotypic oligomerization with IKKα.

FIG. 9: A) Expression of the C-terminal 213 amino acid segment of NIK interrupts the assembly of NIK and IKKα. B) Myc-NIK and the Myc-N1-200 and Myc-N735-947 peptides are comparably expressed in transfected cultures.

FIG. 10: The amino acid and nucleic acid sequences of NIK (SEQ ID NO.1; SEQ ID NO. 2).

FIG. 11: κB-specific gene expression induce by anti-CD3-CD28 stimulation is inhibited by expression of the NIK (735-947) peptide but not by the NIK (1-220) peptide.

DETAILED DESCRIPTION OF THE INVENTION

Terminology

The term “NIK” used herein is defined as a wild-type NF-κB inducing kinase having serine/threonine kinase activity, and having the amino acid sequence as described in FIG. 10 and SEQ ID NO.:1 The nucleotide sequence of NIK is described in SEQ ID NO:2.

The term “mutant NIK” used herein is defined as a NIK protein that inhibits activation of NF-κB-dependent gene expression. Two categories of mutant NIK proteins are described in the present invention and are further defined below.

The term “N-terminus deletion mutant of NIK” used herein is defined as a NIK protein lacking the N-terminus and having at least the C-terminus section that interacts with IKK protein. The N-terminus deletion mutant of NIK includes N-terminus truncation mutants of NIK, and C-terminal NIK peptides that interact with IKK protein. These mutant NIK proteins may or may not retain the catalytic kinase domain of NIK. Specific examples include, but are not limited to, the following N-terminus deletion mutants of NIK: (see FIG. 10 for amino acid sequence of NIK): N350-947 (includes amino acids His350 through Pro947), N570-947 (includes amino acids Gly570 through Pro947), N624-947 (includes amino acids Pro624 through Pro 947), N735-947 (includes amino acids Glu735 through Pro947), N735-813 (includes amino acids Glu735 through Pro8l3), N814-947 (includes amino acids Ser814 through Pro947), and N847-947 (includes Ala847 through Pro947).

The term “kinase-deficient mutant of NIK protein” used herein is defined as a mutant NIK protein that does not exhibit catalytic kinase activity. The terms “catalytically inactive”, “biologically inactive”, and “kinase-deficient” define a NIK protein that does not undergo auto- or trans-phosphorylation. Such phosphorylation may involve either inter- or intra-molecular phosphorylation of the activation loop of NIK which corresponds to amino acids 534-566 which controls phosphorylation activity of NIK. Additionally, the kinase-deficient mutant NIK protein does not activate IKK. The kinase-deficient phenotype of this mutant NIK protein may be due to mutations that occur within the so-called activation loop of NIK. Specific examples include, but are not limited to, the following kinase-deficient NIK mutants: a mutant NIK protein that has three amino acid substitutions Ser-549, Thr-552, and Thr-559 all replaced with alanine residues (NIK-STT549/552/559AAA); or a mutant NIK protein that has Threonine-559 substituted with alanine (NIK-T559A). A second type of kinase deficient mutant of NIK corresponds to a mutant NIK protein that has Lys-429 and Lys-430 replaced with alanine residues (NIK-KK429/430AA). This mutant is altered at the ATP binding site of the kinase and consequently cannot mediate phosphorylation.

The term “IKK” used herein is defined as the Iκ-B-specific kinases, IKKα and IKKβ.

The term “activation of an IKK protein” used herein is defined as changing an inactive IKK protein into an IKK protein that is an IκB kinase. The activated IKK phosphorylates serine 32 and serine 36 of IκB which marks this inhibitor for ubiquitination and degradation.

The term “NIK/IKK” interaction used herein is defined as NIK/IKK protein binding, a NIK/IKK protein complex and NIK/IKK protein assembly.

The term “inhibition of NIK/IKK interaction” used herein is defined as inhibiting either the formation of a NIK/IKK protein complex or disruption of a formed NIK/IKK protein complex.

The term “NF-κB” used herein is defined as a ubiquitously expressed family of eukaryotic transcription factors, comprising a homo- or hetero-dimer of DNA-binding proteins related to the proto-oncogene c-Rel, that controls the expression of many κB-dependent immmune, inflammatory, and anti-apoptotic response genes.

The term “NF-κB-dependent gene expression” used herein is defined as those immune and inflammatory genes that are under the regulatory control of the κB-enhancer. In most cells, NF-κB exists in a latent state in the cytoplasm bound to inhibitory proteins, collectively called IκB, that mask the nuclear localization signal thereby preventing nuclear translocation. The latent form of NF-κB can be induced by cytokines, such as TNFα and IL-1. Both TNFα and IL-1 signaling leads to sequential phosphorylation and activation of a series of proteins involved in a cascade pathway that requires NIK/IKK protein interaction and IKK activation, that in turn leads to phosphorylation and degradation of IκB. Degradation of the IκB inhibitor unmasks the nuclear localization signal of the NF-κB complex allowing its rapid translocation into the nucleus where it engages cognate κB-enhancer elements and activates the transcription of various NF-κB-dependent genes involved in inflammation and immune response.

Mutant NIK

The present invention provides mutant NIK proteins. In one embodiment, the NIK mutant protein is an N-terminus deletion mutant of NIK or a C-terminal NIK peptide that has at least the C-terminus section of NIK which binds to an IKK protein. The N-terminus deletion mutant NIK protein or the C-terminal NIK peptide can have some but not all of the N-terminus section. The N-terminus deletion mutant NIK protein or the C-terminal NIK peptide can also have the central sections of NIK. But the N-terminal deletion mutant NIK protein or the C-terminal NIK peptide must have at least the C-terminus section of NIK that binds to the IKK protein. In particular, one embodiment provides an N-terminus deletion mutant NIK protein or a C-terminal NIK peptide that has an amino acid sequence beginning with glutamic acid at position 735 and ending with proline at position 947 of the wild-type NIK sequence; in the present invention, this mutant is called N735-947. The present invention is not limited to only the N-terminus deletion mutant NIK protein N735-947, as the present invention also provides for other N-terminus deletion mutant proteins that create a mutant NIK protein that can interact with an IKK protein.

In another embodiment the NIK mutant protein is a kinase deficient mutant NIK protein. The kinase deficient mutant phenotype includes a NIK protein that does not undergo auto- or trans-phosphorylation. The kinase deficient phenotype also includes a NIK protein that does not phosphorylate or activate an IKK protein. Normally, a kinase-active NIK protein will phosphorylate an IKK protein which activates the IKK protein to become an IκB kinase. Therefore, an activated IKK is an IκB kinase. The present invention provides two kinase deficient mutant NIK protein sequences that differ from the wild-type NIK protein sequence. In particular, one of the kinase deficient mutant NIK proteins has the amino acid residue threonine-559 substituted with an alanine residue; in the present invention, this mutant is called NIK-T559A. A second kinase deficient NIK mutant has three amino acid residues substituted: the amino acid residues serine-549, and threonine-552, and threonine-559 are each substituted with alanine; in the present invention, this mutant is called NIK-SST549/552/559AAA. And another kinase deficient NIK mutant has two amino acid substitutions, with lysine-429 and lysine-430 substituted with an alanine residue; in the present invention, this mutant is called NIK-KK429/430AA. The present invention is not limited to only the kinase deficient NIK mutants listed above, as the present invention also provides for other amino acid substitutions that create a mutant NIK protein that has the kinase deficient phenotype.

The invention further provides nucleic acid molecules encoding the mutant NIK proteins of the present invention. In one embodiment, the nucleic acid is cDNA. Further, the invention provides a vector, which comprises the nucleic acid molecule of the present invention. Additionally, the invention provides a host vector system. This comprises the vector of the invention in a suitable host cell, e.g., a bacterial cell or eukaryotic cell.

The invention also provides methods for producing the mutant NIK proteins of the present invention. This comprises culturing the host vector system of the invention under suitable culture conditions so as to produce the mutant NIK protein in the host and recovering the mutant NIK protein so produced. The present invention also provides mutant NIK proteins produced by the method above.

The invention provides mutant NIK proteins that are labeled with a detectable marker or conjugated to a second molecule, such as a membrane permeable agent or detectable marker, and used for targeting the second molecule to NIK's target, e.g., IKK. Suitable detectable markers include, but are not limited to, a fluorescent compound, a bioluminescent compound, and chemiluminescent compound.

Methods of the Invention

Activation of NF-κB-dependent gene expression is associated with NIK/IKK interaction and activation of IKK by NIK. The invention provides methods for inhibiting activation of NF-κB-dependent gene expression, by inhibiting the NIK/IKK interaction or by inhibiting the activation of IKK by NIK, using the mutant NIK proteins of the present invention.

One embodiment of the invention provides a method for inhibiting activation of NF-κB-dependent gene expression by inhibiting NIK/IKK interaction, by contacting an IKK protein with a catalytically inactive NIK protein that continues to interact with and bind to IKK. The inhibition of the NIK/IKK interaction includes inhibiting the formation of a NIK/IKK complex, or disruption of a formed NIK/IKK complex. One particular embodiment of the present invention provides a method for inhibiting activation of NF-κB-dependent gene expression by inhibiting wild type NIK/IKK interaction, by contacting the wild type IKK/NIK protein complex with a catalytically inactive or mutant NIK protein, such that the mutant NIK competes with the wild type NIK for assembly with the IKK, thereby forming an inactive NIK/IKK protein complex. One embodiment provides using an N-terminus deletion mutant NIK protein, such as N735-947, to inhibit NIK/IKK interaction. These N-terminus mutant NIK proteins bind to IKK protein and inhibit wild type NIK/IKK interaction, thereby inhibiting activation of NF-κB-dependent gene expression. The methods of the present invention are not limited to using only the N-terminus deletion mutant NIK protein N735-947, as the present invention also provides for use of other N-terminus deletion mutant NIK proteins and other types of NIK mutant proteins that can interact with an IKK protein to inhibit activation of NF-κB-dependent gene expression.

One embodiment of the invention provides a method for inhibiting activation of NF-κB-dependent gene expression, by using a kinase-deficient NIK mutant protein. The kinase deficient phenotype includes a NIK protein that does not undergo auto- or trans-phosphorylation. The kinase deficient phenotype also includes a NIK protein that does not phosphorylate or activate an IKK protein. Normally, a kinase-active NIK protein will phosphorylate an IKK protein thereby activating the IKK protein to become an IκB kinase. Therefore, an activated IKK is an IκB kinase. In particular, the present invention uses NIK proteins that have the kinase deficient phenotype, such as NIK-SST549/552/559AAA or NIK-T559A to inhibit activation of NF-κB-dependent gene expression. The methods of the present invention are not limited to using only the kinase deficient NIK mutants listed above, as the present invention also provides for other mutant NIK proteins that have the kinase deficient phenotype.

The following examples are presented to illustrate the present invention and to assist one of ordinary skill in making and using the same. The examples are not intended in any way to otherwise limit the scope of the invention.

EXAMPLE 1

Analysis of Kinase-Defective Mutants of NIK

NIK protein is a member of the family of mitogen activated protein kinase kinase kinases (MAP3Ks). Three amino acid residues located within the activation loop of the NIK kinase domain are highly conserved among MAP3Ks (Alessi et al 1994; Siow et al 1997; Yan and Templeton 1994; Zheng and K. L. Guan 1994). These amino acid residues correspond to Ser-549, Thr-552 and Thr-559 in the NIK sequence (FIG. 2A). A mutant NIK, called NIK-SST549/552/559AAA, was generated in which Ser-549, Thr-552 and Thr-559 were replaced with alanine residues. A second NIK mutant, called NIK-KK429/430AA, was altered at the ATP binding site of the NIK kinase domain. These mutant NIKs and wild-type NIK were compared for their ability to stimulate κB-dependent luciferase reporter activity in transfected human 293 embryonic kidney cells (see Material and Methods section for details of transfection method).

The results demonstrated that wild-type NIK strongly stimulated luciferase activity (FIG. 2B, closed bars). Additional stimulation of these cultures with TNFα (FIG. 2B, open bars) only weakly augmented the κB-luciferase activity, suggesting that the ectopically expressed NIK was almost fully induced. In contrast, the NIK mutants NIK-SST549/552/559AAA and NIK-KK429/430AA displayed very little spontaneous functional activity (FIG. 2B, closed bars), and both mutant NIKs functioned as dominant-negative inhibitors effectively blocking NF-κB activation induced by either TNFα or wild-type NIK FIG. 2B, open bars).

To further explore the molecular basis for NIK activation, in vivo phosphorylation of wild-type and inactive mutant NIK proteins were compared by metabolic radiolabeling with ³²P-labeled orthophosphoric acid. The radiolabeling procedure described in Material and methods section was used, except that after radiolabeling for 2 hours, cells were cultured in medium either in the presence or the absence of TNFα (20 ng/ml) for 15 minutes, and then NIK was immunoprecipitated with anti-Myc antibodies.

The results demonstrated significant in vivo phosphorylation of wild-type NIK but sharply diminished phosphorylation of the biologically inactive NIK-KK429/430AA and NIK-SST549/552/559AAA (FIG. 2C, top). Addition of TNFα did not enhance the level of phosphorylation of wild-type of mutant NIKs (FIG. 2C, lanes 4 through 6). The observed decrease in phosphorylation of the two mutant NIKs was not explained by marked instability of these proteins, since immunoblotting revealed only slightly lower levels of expression for each (FIG. 2C, bottom) and the half-lives of the mutant NIK proteins is similar to that of wild-type NIK.

Together, these results show that NIK induction of NF-κB correlates with its ability to undergo auto- or trans-phosphorylation in vivo. Furthermore, phosphorylation likely involves either inter- or intra-molecular phosphorylation of the activation loop of NIK. Thus, the NIK mutants NIK-KK429/430AA and NIK-SST549/552/559AAA are kinase-deficient NIK mutants.

EXAMPLE 2

Threonine 559 Plays a Critical Role in the Regulation of NIK Function

To further determine which serine or threonine residue in the activation loop of NIK (e.g. amino acids 534-566, see FIG. 2A) is critical for the regulation of its function, a set of individual mutant NIK proteins were generated. These mutant NIK proteins contained alanine substituted for either a key conserved serine or threonine residues in this loop: NIK-S549A, NIK-T552A and NIK-T559A. These mutant NIK proteins were transfected into 293 cells and evaluated for their ability to activate the downstream kinase IKKA, and to induce NF-κB-dependent transcription.

293 cells were transfected according to the procedure described in Material and methods section below. 20 hours after transfection, in vitro kinase reactions were performed by using anti-IKKβ immunoprecipitates prepared from these cell lysates (FIG. 3A). GST-IκBα (1-62) was added as an exogenous substrate. The kinase reactions were analyzed by SDS-PAGE, followed by transfer to a nitrocellulose membrane and autoradiography. The phosphorylated GST-IκBα substrate is indicated on the right of FIG. 3A. The lower panels show the amounts of immunoprecipitated IKKα and expressed NIK present in each of the cell lysates.

For the functional assays, 293 cells were co-transfected (see Material and methods section below) with 200 ng of κB-luciferase and 100 ng of β-galactosidase reporter plasmids (6RZ), together with 1 μg of expression vector (pRK6) containing either wild-type NIK or mutant NIK-SST549/552/559/AAA, NIK-S549A, NIK-T552A or NIK-T59A. All transfections included the 6RZ plasmid to normalize for differences in gene transfer efficiency by assay of β-galactosidase activity. Twenty hours after transfection, the cultures were stimulated with or without TNFα (20 ng/ml) for 6 hours. Cell lysates were prepared from the cultures, and the luciferase activity present in these lysates was determined as described in Material and methods section below.

The results show that mutants NIK-S549A and NIK-T552A functioned similarly to wild-type NIK. However, the mutant NIK-T559A failed to induce IKKα activity (FIG. 3A) or N-κB-luciferase activity (FIG. 3B).

To determine whether the inability of the NIK-T559A mutant protein to activate IKKα and NF-κB-dependent transcription was due to its failure to phosphorylate IKKα, vectors encoding kinase-deficient IKKα (K44M) were co-transfected with vectors encoding wild type NIK or the inactive T559A mutant of NIK (FIG. 4A). Then, IKKα was immunoprecipitated and subjected to an immunocomplex kinase reaction to test the ability of co-immunoprecipitated NIK to phosphorylate IKKα.

The results demonstrated that wild-type NIK and mutant NIK-S549A and NIK-T552A effectively phosphorylated the coimmunoprecipitated IKKα (K44M) protein in vitro (FIG. 4A). In contrast, the mutant NIK-T559A assembled normally with IKKα (FIG. 3A, bottom) but failed to phosphorylate the coprecipitating IKKα (FIG. 4A, lane 5). In addition, NIK-T559A also lacks the ability for auto-phosphorylation compared to the other NIK activation loop mutant proteins (FIG. 4B, lane 5).

Together, these results show that Thr-559 corresponds to a key regulatory residue within the activation loop of NIK that is essential for NIK function. Thus, NIK-T559A is a kinase-deficient NIK mutant protein.

EXAMPLE 3

Ectopically Expressed NIK Spontaneously Forms Homotypic Oligomers In Vivo

To determine if expressed NIK exists as monomeric or assembled homotypic oligomers in vivo, two different epitope-tagged versions of NIK, Myc-NIK and NIK-T7, were co-transfected into HeLa cells. Lysates from these transfected cells were then sequentially immunoprecipitated with anti-T7 antibodies and immunoblotted with anti-Myc antibodies.

HeLa cells were transiently transfected with plasmids encoding T7- and Myc-epitope-tagged versions of NIK, as described later in Material and Methods. After 24 hours of culture, a portion of the cells were treated with TNFα for 5 or 10 minutes, as indicated in FIG. 5A. Cell lysates were prepared from the cultures and subjected to immunoprecipitation (IP) with anti-T7 antibody conjugated to agarose beads. The immunoprecipitates were then analyzed by immunoblotting with anti-Myc antibodies. Aliquots of the whole-cell lysates (10 μl) were subjected to SDS-PAGE and immunoblotted with anti-T7 or anti-Myc antibodies to determine the levels of Myc-NIK and NIK-T7 expression. In addition, the biological activity of the added TNFα was confirmed by induced degradation of endogenous IκBα detected by immunoblotting with antibodies specific for the C-terminus of IκBα.

The results demonstrated that, when NIK-T7 and Myc-NIK were coexpressed, the two proteins were effectively coimmunoprecipitated (FIG. 5A, lane 2). In addition, stimulation of these cultures for 5 or 10 minutes with TNFα did not further enhance NIK oligomerization (FIG. 5A, lanes 3 and 4). However, the added TNFα was biologically active, since it induce the partial degradation of endogenous IκBα observed at 10 minutes (FIG. 5B). The immunoblotting results demonstrated that the Myc-NIK and NIK-T7 protein were expressed at comparable levels in the transfected cultures (FIG. 5B, lane 2).

Collectively, these results show that biologically active NIK forms dimers or higher order oligomers in vivo.

EXAMPLE 4

Mapping the NIK Domains Involved in Homotypic Oligomerization

To determine which subregions of NIK mediate the homotypic interaction, a series of nested deletion mutant forms of NIK protein were prepared and tested. Each of the deletion mutant NIKs contained an N-terminal Myc epitope tag, and each was stably expressed in 293 cells cotransfected with NIK-T7 (FIG. 6B, lanes 3-11). Cell lysates were immunoblotted with anti-Myc and anti-T7 to verify protein expression levels.

24 hours after transfection, cell lysates were prepared, subjected to SDS-PAGE, and blotted with anti-Myc or anti-T7 antibodies to determine protein expression levels (FIG. 6B). To detect the presence of oligomers formed between mutant NIK proteins and NIK-T7, aliquots of cell lysates were subjected to immunoprecipitation (IP) with anti-T7 antibody conjugated to agarose beads. The immunoprecipitates were subjected to SDS-PAGE and immunoblotted with anti-Myc antibodies (FIG. 6C).

The results demonstrated that, with the exception of Myc-N1-200 and Myc-N570-947, the deletion mutant forms of NIK protein formed oligomers with NIK-T7, as indicated by their coimmunoprecipitation with anti-T7 antibodies (FIG. 6C, lanes 2-11). The results also demonstrated that NIK amino acid residues 570 to 974 failed to oligomerize, although a shorter NIK fragment containing amino acid residues 735 to 947 did form oligomers. It is possible that the 570-947 NIK fragment has an altered protein conformation due to the presence of multiple proline residues between 672 and 759.

EXAMPLE 5

Functional Effects of the C-Terminus of NIK on TNFα and Wild-Type NIK-Induced NF-κB Activation

To determine the intrinsic biological function of deletion mutant forms of NIK proteins and their effects on TNF-α and NIK activation of NF-κB, 293 cells were cotransfected with a NIK deletion mutant and the κB luciferase reporter plasmid, using the method described in the Material and Methods section below. Briefly, 3 μg of expression vectors encoding a NIK deletion mutant was cotransfected into 293 cells, together with κB-luciferase and β-galactosidase reporter plasmids. 20 hours after transfection, the cultures were stimulated with or without TNFα (20 ng/ml) (FIG. 7A) or 0.3 μg of a wild-type NIK expression vector (FIG. 7B) for 6 hours (TNFα induction) or 24 hours (wild-type NIK induction). Cell lysates were prepared and the luciferase activities of these lysates were determined.

The results demonstrated that only the N200-947 mutant form of NIK retained significant, albeit weak, stimulatory activity, in the absence of induction from TNFα or wild-type NIK (FIG. 7A and B, closed bars). When tested in the presence of TNF-α or wild type NIK as an inducer, the C-terminal deletion mutant forms of NIK (N1-366, N1-578 and N1-624) produced only modest and various degrees of inhibition (FIG. 7A and B, open bars). In contrast, each of the N-terminus deletion mutant forms of NIK (N350-947, N578-947, N624-947 and N735-947) markedly inhibited both TNF-α and wild-type NIK induction of κB-luciferase activity.

These results confirm and extend previous studies (Malinin et al 1997) that showed residues 624 to 947 of NIK exert inhibitory effects on TNF-α signaling. Malinin previously showed that TRAF-2 interaction with NIK involves C-terminal sequences located between amino acids 624 and 947. The results presented here show that NIK interaction with IKKα similarly involves the C-terminus of NIK, specifically, an overlapping subregion encompassing residues 735 to 947.

To determine which sequences of the 213-amino acid C-terminal region of NIK are required for inhibition of κB-activity, additional N-terminus deletion mutant forms of NIK (N735-813, N814-947 and N847-947) were prepared and analyzed for their ability to induce κB-luciferase expression (FIG. 7C). The co-transfection and induction methods used for this experiment are described for FIGS. 7A and B above.

The results demonstrated that none of the smaller C-terminal fragments of NIK induced an increase in κB-luciferase activity when added alone (FIG. 7C). Furthermore, none of the smaller C-terminal fragments exerted potent inhibitory effects on TNF-α-induced (FIG. 7C, left graph) or on wild type NIK-induced NF-κB-driven luciferase activity (FIG. 7C, right graph).

Thus a 213 amino acid fragment of NIK, containing the carboxyl terminus of NIK including amino acids 735 to 947, represents the smallest fragment thus far identified which potently inhibits TNF-α mediated activation on NF-κB.

EXAMPLE 6

The C-Terminus of NIK Mediates Binding to IKKα, the IκB-Specific Kinase

To further explore the biological basis for the significant inhibitory effects of the C-terminal region of NIK (N735-947) on TNF-α signaling, the potential role of this region in NIK binding to IKKα was examined.

IKKα-T7 was coexpressed with the various Myc-NIK deletion mutants followed by coimmunoprecipitation with anti-T7 antibodies and immunoblotting with anti-Myc antibodies (FIG. 8). In this experiment, the kinase-deficient mutant, NIK-KK429/430AA (see Example 1, FIG. 2B), was used in place of the wild-type NIK to avoid potential phosphorylation of IKKα which might weaken the NIK-IKKα interaction. 293 cells were cotransfected with IKKα-T7 and Myc-NIK or a deletion form of NIK (Myc-NIK), using the method described in Material and Methods section below. Briefly, the immunoblotting experiment was performed as follows. 24 hours after transfection, cell lysates were prepared, subjected to SDS-PAGE, and immunoblotted with anti-Myc antibodies or anti-T7 antibodies to determine the overall level of expression of the individual proteins (FIG. 8A). Aliquots of the cell lysates were subjected to immunoprecipitation (IP) with anti-T7 antibodies conjugated to agarose beads. The immunoprecipitates were then subjected to SDS-PAGE and immunoblotted with anti-Myc antibodies (FIG. 8B).

The results demonstrated that all of the deletion mutant forms of NIK and T7-IKKα were comparably expressed in these transfection experiments (FIG. 8A). The results also demonstrated that the kinase-deficient NIK mutant (Myc-NIK-KK429/430A) interacts with IKKα, as shown by the coimmunoprecipitation results (FIG. 8B, lane 2). Furthermore, the results demonstrated that none of the C-terminus deletion mutant forms of NIK assembled with IKKα (FIG. 8B, lanes 3-7), while all of the N-terminus deletion mutant proteins, including N735-947, effectively associated with IKKα (FIG. 8B, lanes 8-11).

EXAMPLE 7

Expression of the C-Terminal 213-Amino-Acid Segment of NIK Interrupts the Assembly of NIK and IKKα

To determine if expression of the 213-amino-acid C-terminal fragment of NIK (N735-947) is sufficient to disrupt the interaction of NIK and IKKα, cells were cotransfected with Myc-NIK and IKKα-T7, and with either Myc-N735-947 or Myc-N1-220. The Myc-N1-220 construct expresses a comparably-sized peptide containing the N-terminus of NIK (residues 1 to 220), and was used as a control in this experiment. 293 cells were cotransfected using the method described in the Material and Methods section below. Briefly, the immunoblotting experiment was performed as follows. 24 hours after transfection, cell lysates were prepared from the transfected cultures. Aliquots of the cell lysates were subjected to immunoprecipitation (IP) with anti-T7 antibodies conjugated to agarose beads. The immunoprecipitates were then subjected to SDS-PAGE and immunoblotted with anti-Myc antibodies (FIG. 9A). Aliquots of the cell lysates were subjected to SDS-PAGE and immunoblotted with anti-Myc antibodies to assess the expression of the individual proteins (FIG. 9B).

The results demonstrated that the N-terminus deletion NIK mutant, containing NIK residues 735 through 947 (Myc-N735-947) effectively blocked the physical association of IKKα (IKKα-T7) with NIK (Myc-NIK) (FIG. 9A, lane 3), since a NIK/IKKα complex did not immunoprecipitate when the N-terminal fragment of NIK was coexpressed. The results also demonstrated that full-length NIK (Myc-NIK) and the two NIK fragments (Myc-N1-220 and Myc-N735-947) were comparably expressed in these transfected cultures (FIG. 9B). Furthermore, the results demonstrated that the N-terminal fragment of NIK (Myc-N1-200) did not block NIK/IKKα association.

Collectively, the results presented in FIGS. 8 and 9 show that the C-terminus of NIK, containing amino acids 735 through 945, corresponds to a binding domain for IKKα that is both necessary and sufficient for NIK binding to IKKα. Additionally, in TNFα signaling assays, the C-terminal fragment of NIK prevents effective assembly of NIK and IKKα, resulting in inhibition of NF-κB-dependent activation.

EXAMPLE 8

Expression of the C-Terminal 213 Amino Acid Segment of NIK Interrupts CD3-CD2 Costimulatory Signaling

The activation of T cells requires two signals involving binding of antigen to the T cell receptor and the binding of B7 ligands to CD28 receptors on T cells. Binding of these receptors promotes the activation of IL-2 gene expression which is dependent on NF-κB/c-Rel induction. Binding of these receptors includes binding of the receptor to its cognate ligand, or ligation of the receptor with antibody. Our recent studies now demonstrate that the NIK 735-947 effectively inhibits CD3-CD28 mediated co-stimulation of a composite enhancer element present in the IL-2 gene (FIG. 11). In contrast, a similarly sized N-terminal peptide, NIK 1-200, was without effect. These findings indicate that the C-terminal domain of NIK forms not only an effective inhibitor of TNFα stimulation, but also of immune activation mediated through the T cell receptor CD3 complex and the CD28 co-receptor.

MATERIAL AND METHODS

Expression Vector, Biological Reagents, and Cell Lines

Plasmid κB-TATA-luciferase has been previously described (S.-C. Sun et al 1996). The LacZ reporter construct containing the Rous sarcoma virus long terminal repeat (6RZ) was obtained from D. Pearce (University of California, San Fransisco).

The full-length NIK cDNA was generated in three fragments by reverse transcription-PCR using Jurkat E6-1 MRNA and three pairs of primers (see Lin et al 1998 for sequence of primers) based on the sequence published by Malinin et al (Malinin et al 1997). The PCR fragments were subcloned into pBluescript, and the full-length NIK cDNA was reconstituted by sequentially subcloning the fragments into the pRK vector (provided by Allan Hall, University College London) in frame with an N-terminal Myc epitope tag. The resulting full-length NIK cDNA was designated pRK-Myc-NIK. The full-length NIK cDNA was further subcloned into pEV3S in frame with a C-terminal T7 epitope tag and was designated pEV-NIK-T7. The two kinase domain NIK mutants, NIK-KK429/430AA and NIK-S549A/T552A/T559A, were generated by overlapping PCR. Murine IKKα/CHUK has been described previously (Connelly and Marcu 1995) and was subcloned into pEV3S in frame with a C-terminal T7 epitope to generate pEV-IKKα-T7. Recombinant human TNFα was purchased from Endogen (Cambridge, Mass.) HeLa and 293 cells were maintained in Dulbecco modified Eagle medium supplemented with 10% heat-inactivated fetal bovine serum, penicillin, and streptomycin.

Transfections and Reporter Gene Assays

293 cells (5×10⁵ cells/well) were seeded into six-well (35 mm diameter) plates and transfected the following day with 4 μg of DNA by the calcium phosphate precipitation method (Sambrook, Fritz and Maniatis 1989). Cells were co-transfected with plasmid κB-TATA-luciferase (S.-C. Sun et al 1996), the LacZ reporter construct containing the Rous sarcoma virus long terminal repeat (6RZ) (obtained from D. Pearce University of California, San Francisco), and an expression vector (pEV3S) containing wild-type or mutant NIK subcloned in-frame with a C-terminal T7 epitope tag. All transfections included the 6RZ plasmid to normalize for differences in gene transfer efficiency by assay of β-galactosidase activity. The mutant NIKs were generated by overlapping PCR. After 15 to 20 hours, selected cultures were stimulated with TNFα (20 ng/ml) for 6 hours. Luciferase activity was typically measured 20 to 25 hours after transfection using the enhanced luciferase assay kit and a Monolight 2010 luminometer (Analytical Luminescence Laboratory, Ann Arbor, Mich.). Data were presented as fold induction of luciferase activity ± the standard deviations derived from independent triplicate transfections.

Immunoprecipitation

Immunoprecipitation was performed by lysing the transfected cells 24 hours later in ELB buffer containing 1.5% Nonidet P-40, 250 mM NaCl, 50 mM HEPES (pH=7.4), 1 mM EDTA, and the following protease inhibitors: 1 mM phenylmethylsulfonyl fluoride, 5 μg/ml antipain, 5 μg/ml aprotinin, 5 μg/ml leupeptin, 0.5 μg/ml pepstatin, 7.5 μg/ml bestatin, 4 μg/ml phosphoroamidon, and 5 μg/ml trypsin inhibitor. Lysates were immunoprecipitated with anti-T7-Tag antibody linked to agarose beads (Novagen, Madison, Wis). Immnunoprecipitates were washed three times in lysis buffer and then subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), followed by transfer to nitrocellulose membranes and immunoblotting with anti-Myc-Tag antibodies (Santa Cruz Biotechnology, Santa Cruz, Calif.).

Immune Complex Kinase Assays

For the immune complex kinase assays, transfected cells were lysed 12 to 18 hours post-transfection, and immunoprecipitated with antibodies and protein A-agarose beads, as described above. Immunoprecipitated beads were further washed with kinase buffer containing 10 mM HEPES (pH=7.4), 1 mM MnCl₂, 5 mM MgCl₂, 12.5 mM β-glycero-2-phosphate, 50 μM Na₃VO₄, 2 mM NaF, and 50 μM dithiothreitol. After suspension in 20 μl of kinase buffer, the immunoprecipitates were incubated with 5 μCi of [γ-³²P]ATP (6000 Ci/mmol) with or without 1 μg of recombinant glutathione S-transferase (GST)-IκBα (1-62) as an exogenous substrate for 30 minutes at 30° C. The reaction was terminated by the addition of SDS sample buffer. The samples were analyzed by SDS-PAGE, followed by transfer to nitrocellulose membranes and exposure to Hyperfilm MP (Amersham Life Sciences). The membranes were subsequently probed with antibodies to determine the amount of immunoprecipitated quinces.

In Vivo Radiolabeling With ³²P-Labeled Orthophosphoric Acid

24 hours after transfection, the cells were washed once in phosphate-free Dulbecco modified Eagle medium (Life Technologies) supplemented with 10% dialyzed, heat-inactivated fetal bovine serum and starved for 1 hour in the same medium. ³²P-labeled orthophosphoric acid (0.5 mCi) was then added to the cells. After incubation for 2 hours, the cells were lysed in ELB buffer and immunoprecipitated with anti-Myc-Tag antibody and protein A-agarose as described above. Immunoprecipitates were analyzed by SDS-PAGE, followed by transfer to nitrocellulose membranes and exposure to Hyperfilm MP. Immunoblotting was performed with anti-Myc-Tag antibodies to assess the levels of immunoprecipitated NIK proteins.

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2 1 947 PRT NF-KAPPA B INDUCING KINASE (NIK) 1 Met Ala Val Met Glu Met Ala Cys Pro Gly Ala Pro Gly Ser Ala Val 1 5 10 15 Gly Gln Gln Lys Glu Leu Pro Lys Pro Lys Glu Lys Thr Pro Pro Leu 20 25 30 Gly Lys Lys Gln Ser Ser Val Tyr Lys Leu Glu Ala Val Glu Lys Ser 35 40 45 Pro Val Phe Cys Gly Lys Trp Glu Ile Leu Asn Asp Val Ile Thr Lys 50 55 60 Gly Thr Ala Lys Glu Gly Ser Glu Ala Gly Pro Ala Ala Ile Ser Ile 65 70 75 80 Ile Ala Gln Ala Glu Cys Glu Asn Ser Gln Glu Phe Ser Pro Thr Phe 85 90 95 Ser Glu Arg Ile Phe Ile Ala Gly Ser Lys Gln Tyr Ser Gln Ser Glu 100 105 110 Ser Leu Asp Gln Ile Pro Asn Asn Val Ala His Ala Thr Glu Gly Lys 115 120 125 Met Ala Arg Val Cys Trp Lys Gly Lys Arg Arg Ser Lys Ala Arg Lys 130 135 140 Lys Arg Lys Lys Lys Ser Ser Lys Ser Leu Ala His Ala Gly Val Ala 145 150 155 160 Leu Ala Lys Pro Leu Pro Arg Thr Pro Glu Gln Glu Ser Cys Thr Ile 165 170 175 Pro Val Gln Glu Asp Glu Ser Pro Leu Gly Ala Pro Tyr Val Arg Asn 180 185 190 Thr Pro Gln Phe Thr Lys Pro Leu Lys Glu Pro Gly Leu Gly Gln Leu 195 200 205 Cys Phe Lys Gln Leu Gly Glu Gly Leu Arg Pro Ala Leu Pro Arg Ser 210 215 220 Glu Leu His Lys Leu Ile Ser Pro Leu Gln Cys Leu Asn His Val Trp 225 230 235 240 Lys Leu His His Pro Gln Asp Gly Gly Pro Leu Pro Leu Pro Thr His 245 250 255 Pro Phe Pro Tyr Ser Arg Leu Pro His Pro Phe Pro Phe His Pro Leu 260 265 270 Gln Pro Trp Lys Pro His Pro Leu Glu Ser Phe Leu Gly Lys Leu Ala 275 280 285 Cys Val Asp Ser Gln Lys Pro Leu Pro Asp Pro His Leu Ser Lys Leu 290 295 300 Ala Cys Val Asp Ser Pro Lys Pro Leu Pro Gly Pro His Leu Glu Pro 305 310 315 320 Ser Cys Leu Ser Arg Gly Ala His Glu Lys Phe Ser Val Glu Glu Tyr 325 330 335 Leu Val His Ala Leu Gln Gly Ser Val Ser Ser Ser Gln Ala His Ser 340 345 350 Leu Thr Ser Leu Ala Lys Thr Trp Ala Ala Arg Gly Ser Arg Ser Arg 355 360 365 Glu Pro Ser Pro Lys Thr Glu Asp Asn Glu Gly Val Leu Leu Thr Glu 370 375 380 Lys Leu Lys Pro Val Asp Tyr Glu Tyr Arg Glu Glu Val His Trp Ala 385 390 395 400 Thr His Gln Leu Arg Leu Gly Arg Gly Ser Phe Gly Glu Val His Arg 405 410 415 Met Glu Asp Lys Gln Thr Gly Phe Gln Cys Ala Val Lys Lys Val Arg 420 425 430 Leu Glu Val Phe Arg Ala Glu Glu Leu Met Ala Cys Ala Gly Leu Thr 435 440 445 Ser Pro Arg Ile Val Pro Leu Tyr Gly Ala Val Arg Glu Gly Pro Trp 450 455 460 Val Asn Ile Phe Met Glu Leu Leu Glu Gly Gly Ser Leu Gly Gln Leu 465 470 475 480 Val Lys Glu Gln Gly Cys Leu Pro Glu Asp Arg Ala Leu Tyr Tyr Leu 485 490 495 Gly Gln Ala Leu Glu Gly Leu Glu Tyr Leu His Ser Arg Arg Ile Leu 500 505 510 His Gly Asp Val Lys Ala Asp Asn Val Leu Leu Ser Ser Asp Gly Ser 515 520 525 His Ala Ala Leu Cys Asp Phe Gly His Ala Val Cys Leu Gln Pro Asp 530 535 540 Gly Leu Gly Lys Ser Leu Leu Thr Gly Asp Tyr Ile Pro Gly Thr Glu 545 550 555 560 Thr His Met Ala Pro Glu Val Val Leu Gly Arg Ser Cys Asp Ala Lys 565 570 575 Val Asp Val Trp Ser Ser Cys Cys Met Met Leu His Met Leu Asn Gly 580 585 590 Cys His Pro Trp Thr Gln Phe Phe Arg Gly Pro Leu Cys Leu Lys Ile 595 600 605 Ala Ser Glu Pro Pro Pro Val Arg Glu Ile Pro Pro Ser Cys Ala Pro 610 615 620 Leu Thr Ala Gln Ala Ile Gln Glu Gly Leu Arg Lys Glu Pro Ile His 625 630 635 640 Arg Val Ser Ala Ala Glu Leu Gly Gly Lys Val Asn Arg Ala Leu Gln 645 650 655 Gln Val Gly Gly Leu Lys Ser Pro Trp Arg Gly Glu Tyr Lys Glu Pro 660 665 670 Arg His Pro Pro Pro Asn Gln Ala Asn Tyr His Gln Thr Leu His Ala 675 680 685 Gln Pro Arg Glu Leu Ser Pro Arg Ala Pro Gly Pro Arg Pro Ala Glu 690 695 700 Glu Thr Thr Gly Arg Ala Pro Lys Leu Gln Pro Pro Leu Pro Pro Glu 705 710 715 720 Pro Pro Glu Pro Asn Lys Ser Pro Pro Leu Thr Leu Ser Lys Glu Glu 725 730 735 Ser Gly Met Trp Glu Pro Leu Pro Leu Ser Ser Leu Glu Pro Ala Pro 740 745 750 Ala Arg Asn Pro Ser Ser Pro Glu Arg Lys Ala Thr Val Pro Glu Gln 755 760 765 Glu Leu Gln Gln Leu Glu Ile Glu Leu Phe Leu Asn Ser Leu Ser Gln 770 775 780 Pro Phe Ser Leu Glu Glu Gln Glu Gln Ile Leu Ser Cys Leu Ser Ile 785 790 795 800 Asp Ser Leu Ser Leu Ser Asp Asp Ser Glu Lys Asn Pro Ser Lys Ala 805 810 815 Ser Gln Ser Ser Arg Asp Thr Leu Ser Ser Gly Val His Ser Trp Ser 820 825 830 Ser Gln Ala Glu Ala Arg Ser Ser Ser Trp Asn Met Val Leu Ala Arg 835 840 845 Gly Arg Pro Thr Asp Thr Pro Ser Tyr Phe Asn Gly Val Lys Val Gln 850 855 860 Ile Gln Ser Leu Asn Gly Glu His Leu His Ile Arg Glu Phe His Arg 865 870 875 880 Val Lys Val Gly Asp Ile Ala Thr Gly Ile Ser Ser Gln Ile Pro Ala 885 890 895 Ala Ala Phe Ser Leu Val Thr Lys Asp Gly Gln Pro Val Arg Tyr Asp 900 905 910 Met Glu Val Pro Asp Ser Gly Ile Asp Leu Gln Cys Thr Leu Ala Pro 915 920 925 Asp Gly Ser Phe Ala Trp Ser Trp Arg Val Lys His Gly Gln Leu Glu 930 935 940 Asn Arg Pro 945 2 2844 DNA NF-KAPPA B INDUCING KINASE (NIK) 2 atggcagtga tggaaatggc ctgcccaggt gcccctggct cagcagtggg gcagcagaag 60 gaactcccca agccaaagga gaagacgccg ccactgggga agaaacagag ctccgtctac 120 aagcttgagg ccgtggagaa gagccctgtg ttctgcggaa agtgggagat cctgaatgac 180 gtgattacca agggcacagc caaggaaggc tccgaggcag ggccagctgc catctctatc 240 atcgcccagg ctgagtgtga gaatagccaa gagttcagcc ccaccttttc agaacgcatt 300 ttcatcgctg ggtccaaaca gtacagccag tccgagagtc ttgatcagat ccccaacaat 360 gtggcccatg ctacagaggg caaaatggcc cgtgtgtgtt ggaagggaaa gcgtcgcagc 420 aaagcccgga agaaacggaa gaagaagagc tcaaagtccc tggctcatgc aggagtggcc 480 ttggccaaac ccctccccag gacccctgag caggagagct gcaccatccc agtgcaggag 540 gatgagtctc cactcggcgc cccatatgtt agaaacaccc cgcagttcac caagcctctg 600 aaggaaccag gccttgggca actctgtttt aagcagcttg gcgagggcct acggccggct 660 ctgcctcgat cagaactcca caaactgatc agccccttgc aatgtctgaa ccacgtgtgg 720 aaactgcacc acccccagga cggaggcccc ctgcccctgc ccacgcaccc cttcccctat 780 agcagactgc ctcatccctt cccattccac cctctccagc cctggaaacc tcaccctctg 840 gagtccttcc tgggcaaact ggcctgtgta gacagccaga aacccttgcc tgacccacac 900 ctgagcaaac tggcctgtgt agacagtcca aagcccctgc ctggcccaca cctggagccc 960 agctgcctgt ctcgtggtgc ccatgagaag ttttctgtgg aggaatacct agtgcatgct 1020 ctgcaaggca gcgtgagctc aagccaggcc cacagcctga ccagcctggc caagacctgg 1080 gcagcacggg gctctagatc ccgggagccc agccccaaaa ctgaggacaa cgagggtgtc 1140 ctgctcactg agaaactcaa gccagtggat tatgagtacc gagaagaagt ccactgggcc 1200 acgcaccagc tccgcctggg cagaggctcc ttcggagagg tgcacaggat ggaggacaag 1260 cagactggct tccagtgcgc tgtcaaaaag gtgcggctgg aagtatttcg ggcagaggag 1320 ctgatggcat gtgcaggatt gacctcaccc agaattgtcc ctttgtatgg agctgtgaga 1380 gaagggcctt gggtcaacat cttcatggag ctgctggaag gtggctccct gggccagctg 1440 gtcaaggagc agggctgtct cccagaggac cgggccctgt actacctggg ccaggccctg 1500 gagggtctgg aatacctcca ctcacgaagg attctgcatg gggacgtcaa agctgacaac 1560 gtgctcctgt ccagcgatgg gagccacgca gccctctgtg actttggcca tgctgtgtgt 1620 cttcaacctg atggcctggg aaagtccttg ctcacagggg actacatccc tggcacagag 1680 acccacatgg ctccggaggt ggtgctgggc aggagctgcg acgccaaggt cgacgtctgg 1740 agcagctgct gtatgatgct gcacatgctc aacggctgcc acccctggac tcagttcttc 1800 cgagggccgc tctgcctcaa gattgccagc gagcctccgc ctgtgaggga gatcccaccc 1860 tcctgcgccc ctctcacagc ccaggccatc caagaggggc tgaggaaaga gcccatccac 1920 cgcgtgtctg cagcggagct gggagggaag gtgaaccggg cactacagca agtgggaggt 1980 ctgaagagcc cttggagggg agaatataaa gaaccaagac atccaccgcc aaatcaagcc 2040 aattaccacc agaccctcca tgcccagccg agagagcttt cgccaagggc cccagggccc 2100 cggccagctg aggagacaac aggcagagcc cctaagctcc agcctcctct cccaccagag 2160 cccccagagc caaacaagtc tcctcccttg actttgagca aggaggagtc tgggatgtgg 2220 gaacccttac ctctgtcctc cctggagcca gcccctgcca gaaaccccag ctcaccagag 2280 cggaaagcaa ccgtcccgga gcaggaactg cagcagctgg aaatagaatt attcctcaac 2340 agcctgtccc agccattttc tctggaggag caggagcaaa ttctctcgtg cctcagcatc 2400 gacagcctct ccctgtcgga tgacagtgag aagaacccat caaaggcctc tcaaagctcg 2460 cgggacaccc tgagctcagg cgtacactcc tggagcagcc aggccgaggc tcgaagctcc 2520 agctggaaca tggtgctggc ccgggggcgg cccaccgaca ccccaagcta tttcaatggt 2580 gtgaaagtcc aaatacagtc tcttaatggt gaacacctgc acatccggga gttccaccgg 2640 gtcaaagtgg gagacatcgc cactggcatc agcagccaga tcccagctgc agccttcagc 2700 ttggtcacca aagacgggca gcctgttcgc tacgacatgg aggtgccaga ctcgggcatc 2760 gacctgcagt gcacactggc ccctgatggc agcttcgcct ggagctggag ggtcaagcat 2820 ggccagctgg agaacaggcc ctaa 2844 

What is claimed:
 1. An N-terminus deletion mutant NIK protein, consisting of an amino acid sequence beginning with glutamic acid at position 735 and ending with proline at position 947 of SEQ ID NO:
 1. 2. The N-terminus deletion mutant NIK protein of claim 1, wherein the mutant NIK protein interacts with an IKK protein. 